This invention is in the field of autostereoscopic displays and more particularly to autostereoscopic displays employing a head-mounted projector and retroreflective screen.
Autostereoscopic displays present stereoscopic imagery to an observer with no need for special glasses and are very well known. A class of autostereoscopic displays often referred to as specular displays (see xe2x80x9cMicropolarizer-based multiple-viewer autostereoscopic displayxe2x80x9d by Benton, Slowe, Kropp and Smith in J. O. Merritt, S S. Fisher, and M. T. Bolas, Eds., SPIE Proc. Vol. 3639 Stereoscopic Displays and Virtual Reality Systems VI (SPIE, January 1999) paper 3639-10, page 1) uses large lenses, mirrors or retro-reflectors to direct light from the source to the eyes of the observer.
A problem encountered in specular autostereoscopic displays relates to the need to track the eyes of the observer using an appropriate servo to maintain a condition whereby the light corresponding to the appropriate source images remain fixed on the eyes of the observer. For example, U.S. Pat. No. 5,671,992 by Richards discloses a display unit having a pair of projectors that relay separate stereo images to separate eyes of the observer. Light from the projectors is directed to a beam splitter and then to a retro-reflective screen where it is returned through the beamsplitter to the observer""s eyes. In Richards, tracking and servo means are used to detect eye position and move the projectors to maintain coincidence of the observer""s eyes and the images of the projector""s exit pupils formed by the screen. An approach to the problem of this type requires extensive equipment, displays that must anticipate all possible head positions, limitations of the viewer""s movement and are confined to an audience of one for each display.
A different approach was taught by Masahiko Inami as documented in the ACM SIGGRAPH 99 Conference Abstracts and Applications document, page 179, xe2x80x9cHead-Mounted Projectorxe2x80x9d and by U.S. Pat. No. 5,606,458 granted to Fergason. In these references, viewer-head-mounted projection systems are disclosed that use retro-reflective material to return the projected light from a pair of head-mounted projectors back into the viewer""s eyes. Thus, an automatic registration of the image of the exit pupils of the projectors with the observer""s eyes is achieved. However this method requires mounting not only the projectors upon the head, but also mounting a beam-splitting apparatus before the eyes since the projected beams are reflected from a conventional retro-reflective screen directly back to the source. Wearing beam-splitters reduces the amount of light returning to the eye, is cumbersome and ungainly as well being fragile and possibly dangerous if the viewer collides with an object.
U.S. Pat. No. 4,347,508 to Spooner describes a head-coupled area of interest stereoscopic visual display incorporating a bead-type retro-reflective screen having a surface modified by incorporation of a diffractive overlayer. The overlayer provides a deflection of the retro-reflected light from its conventional trajectory so that the modified retro-reflected light is aligned with the location of the eyes of the observer. The deflection provided by the overlayer is achieved by a diffractive effect. The ""508 patent gives a design of an overlayer suitable for 550 nm or a narrow wavelength range in the vicinity of 550 nm. A single diffractive order of the overlayer grating is directed below the line of incidence and into the viewer""s eyes. Unfortunately, the diffractive deflection of the retro-reflected light is a wavelength sensitive deflection. As is readily apparent, this approach is unsuitable for full color images as the individual spectral components of the light will be returned in different directions. Also, the diffractive approach to retro-reflective screen modification deflects returning light from the line of incidence by a specific angle and so is operative only at a specific viewing distance from the screen.
The display system of the present invention provides a user with the visual perception of peering into a stereoscopic three dimensional scene by projecting left and right images onto a retroreflective screen that has been modified to return the projected light directly to the eye of the observer and by using a dynamic imaging system that responds to movement to alter the scene content in a manner consistent with the observer""s movement.
The present invention provides a superior solution in that the system invented has all the benefits of a head-mounted projection system coupled with retro-reflective display, but by eliminating the need for beam splitters it addresses the previously described shortcomings of encumbrance, lack of brightness, weight and fragility. This is accomplished by using a modified cube-corner retro-reflective material. Normally, cube-corner material reflects a beam back directly along the beam""s source path. By using a deformed cube-corner material, the beam is reflected back along a different path directly to the eye rather than to the projector. Because the modification of the retro-reflective behavior is accomplished by reflection (not diffraction) in the modified cube-corner elements, the modified screen functions properly with multicolor and even with full color images.